The present invention relates in general to the storage of nuclear fuel elements and more particularly to a rack for the storing of spent nuclear fuel elements in a pool for a nuclear power plant.
Heretofore, racks for spent nuclear fuel elements were formed from standard structual members, such as angle bars, I-beams, T-shaped members and channel members. Such racks were manufactured by General Electric Company, Combustion Engineering Company, Inc., PAR Systems, Speedway Machine & Tool Co., Inc., and others. A fuel storage rack sold by PX Engineering Company, Inc. is illustrated in Nuclear News, Mid-April 1974, which appears to employ upright enclosures of a generally square cross-sectional area. The fuel rack sold by Speedway Machine & Tool Co. appears to be formed from upright posts braced by horizontal members spaced apart vertically. The General Electric spent fuel storage rack appears to employ upright I-beams, T-shaped columns and upright channel members.
The delay in the availability of nuclear fuel reprocessing plants have presented the problem to nuclear power plants of being able to transport the spent fuel elements to a reprocessing plant. When a reactor is refueled, the spent fuel elements are stored in the spent fuel storage pool of a nuclear power plant. Spent fuel storage pools for the usual nuclear power plant were designed to store one full reactor core plus one or two discharges of spent nuclear fuel elements. A fuel discharge may be from .20 to .33 of a core loading. It is desirable to always maintain enough space in the spent fuel storage pool to unload the full reactor core. Generally, this would leave space for only one or two discharges of the nuclear fuel elements. A nuclear power plant should have sufficient space for the spent nuclear fuel elements to enable the nuclear power plant to keep operating and refueling until it is possible to transport spent nuclear fuel elements to a reprocessing plant.
Heretofore, spent fuel storage racks have relied on water and physical separation as the primary means of neutron moderation and absorption between nuclear fuel elements. The nuclear fuel elements have been spaced by the rack storing the same so that the effective multiplication factor (K.sub.eff) for the fuel array would remain below the required limit. As a consequence thereof, a large portion of the rack and the spent fuel storage area was occupied by water.
It has been known that a highly effective neutron absorber, such as Boral, can be used between fuel assemblies to reduce fuel element spacing. Boral has a much greater neutron absorption cross-section than water and allows a closer geometric spacing of fuel elements without exceeding the K.sub.eff limit. Brooks & Perkins Corporation sells Boral, which comprises boron carbide particles dispersed in aluminum metal. Cadmium and borated stainless steel have also been used as neutron absorbers.